This invention pertains to thermosetting aqueous dispersed acrylic, melamine resin, and polyvinylidene fluorine polymeric compositions capable of heat curing to form a homogenously cured surface coating.
Hydrofluorocarbon polymers dispersed in organic solvents are known such as disclosed in U.S. Pat. Nos. 3,340,222 and 3,324,069. Such coatings however require major amounts of an organic solvent which in turn causes undesirable pollution and solvent emission problems. Attempts to disperse polyvinylidene fluorocarbons into water dispersed latex emulsions systems such as acrylic latexes to provide highly durable coatings have been unsuccessful. A water dispersed fluorocarbon is shown in U.S. Pat. No. 3,679,618. Curing and coalescense of the latex mixture often produced non-uniform films containing polymer particles dispersed in the film. For example a conventional film forming acrylic latex having a Tg around 20.degree. C. produces a non-homogenous surface coating film containing discreet particles of fluorocarbon polymer. The non-homogenously dispersed fluorocarbon polymer undesirably tends to cause premature film failure at the locale of the particle particularly due to ultraviolet light degradation thus causing poor durability and undesirable film integrity properties. U.S. Pat. No. 4,141,873 discloses an air dry latex polymer containing vinylidene fluorine polymer dispersed therein wherein the latex polymer may coalesce to form a film leaving discreet vinylidene fluorine polymer particles entrapped in said film.
It now has been found that water dispersed high Tg acrylic latex having carboxyl and/or hydroxyl groups or other functional reactive groups in combination with melamine and water dispersed polyfluorohydrocarbon polymer advantageously produces an excellent surface coating composition adapted to cure at temperatures above about 350.degree. F. (177.degree. C.) to produce a homogenous film relatively free of entrapped dispersed fluorocarbon polymer particles. It has been found that by providing a high Tg thermosetting acrylic polymer having a Tg greater than 50.degree. C. advantageously narrows the Tg differential between the acrylic and polyfluorohydrocarbon polymer, which in turn advantageously avoids premature coalescence of the acrylic polymer and avoids isolation of the polyfluorohydrocarbon polymer particles in the cured coalesced surface coating film. The resulting film exhibits excellent film integrity properties including ultraviolet light resistance, elasticity, flexability, toughness, salt spray resistance, adhesion, moisture resistance, and outdoor durability. These and other advantages will become more apparent by referring to detailed description and the illustrative examples.